During intense periods of exercise, where the rate of demand for energy is high, pyruvate resulting from the breakdown of glucose is converted into lactate. This reduction of pyruvate to lactate is beneficial since it regenerates NAD+ for the continuation of glycolytic energy production required by the working muscle. Increased lactate can be removed in a number of ways; it can be exported from the oxygen-deficient cell and taken up by an oxygen-rich cell where it can be oxidized to pyruvate and used directly to fuel the citric acid cycle (Brooks G.A. Mammalian fuel utilization during sustained exercise. Comp Biochem Physiol B Biochem Mol Biol. 1998 May; 120(1):89-107. Review), or it can be reconverted by the liver, through the Cori cycle, to glucose.
The recognition of monocarboxylate transport (MCT) proteins in the mitochondria and the closely associated lactate oxidation complexes (Kirkwood S.P., Munn E.A., Brooks G.A. Mitochondrial reticulum in limb skeletal muscle. Am J. Physiol. 1986 September; 251(3 Pt 1):C395-402), suggests that lactate can be transported and oxidized in the mitochondria of the same cell.
Contrary to popular belief, increased levels of lactate do not directly cause acidosis; an elevated presence of acidic species (Robergs R, Ghiasvand F, Parker D. Biochemistry of exercise-induced metabolic acidosis. Am J Physiol Regul Integr Comp Physiol. 2004; 287:R502-16). Lactate appears to be a consequence rather then the cause of cellular events which cause acidosis. The physiological state of muscle cells are such that lactate never has hydrogen available to decrease pH in the surrounding solution. Acidosis is actually a result of the hydrolysis of ATP, wherein hydrogen ions are released into the surrounding solution. During heavy exercise, ATP is produced and utilized quickly in the cytoplasm causing a rapid decrease in cellular pH. The buffering systems of the tissues are rapidly overcome and pH drops resulting in a state of acidosis.
Additionally, several hours after exercise there are dynamic changes in the rates of both skeletal muscle synthesis and breakdown. The consumption of specific dietary components are known to further influence the response of skeletal muscle to exercise. The main components of food which are known to stimulate increased muscle protein synthesis are amino acids (Rennie M J. Body maintenance and repair: how food and exercise keep the musculoskeletal system in good shape. Exp Physiol. 2005 July; 90(4):427-36). Increased levels of circulating essential amino acids have been shown to stimulate protein synthesis (Smith K, Reynolds N, Downie S, Patel A, Rennie M J. Effects of flooding amino acids on incorporation of labeled amino acids into human muscle protein. Am J Physiol. 1998 July; 275(1 Pt 1):E73-8).
More specifically, the branched-chain amino acids (BCAA) consisting of Leucine, Isoleucine and Valine, are not only used for the synthesis of other amino acids, but are also important in the regulation of anabolic processes in muscle. Furthermore, BCAA not only increase the rate of protein synthesis but also inhibit the rate of protein degradation (Matthews D E. Observations of branched-chain amino acid administration in humans. J Nutr. 2005 June; 135(6 Suppl):1580S-4S).
In situations following extended periods of repetitive, forceful muscular contractions, such as during exhaustive physical exercise, it would be advantageous for an individual to both maintain physiological pH levels and increase cellular concentrations of Leucine. In this regard, the anabolic state of muscle is increased, facilitating shorter recovery periods as well as increasing strength and muscle size.